Flexible catheter

A medical catheter comprising:

• a proximal section having a proximal end and a distal end;
• a transition section having a proximal end and a distal end;
• a distal section having a proximal end and a distal end;
• a balloon having a proximal end and a distal end, the distal end of the proximal section forming the transition section, the distal end of the transition section being coaxially affixed to and covered by the proximal end of the distal section, the distal end of the distal section being affixed to the proximal end of the balloon;
• a guidewire shaft defining a guidewire lumen, the guidewire shaft extending longitudinally and coaxially throughout the proximal section, the transition section, the distal section and the balloon with enough clearance between an outer diameter of the guidewire shaft and an inner diameter of the proximal section, transition section, distal section and balloon so as to define an inflation lumen therebetween and maintain fluid communication with the balloon;
• and
• the transition section further comprising a necked-down area of reduced outer diameter beginning at the proximal end of the transition section, the area of reduced outer diameter having a spirally cut distal portion to increase flexibility and kink resistance, the distal end of the transition section ending proximal to the proximal end of the balloon.